The present invention relates to an arrangement for applying a surface pressure to continuously moving workpiece webs, for example laminates.
More particularly, it relates to such an arrangement which has at least one rotatable pressing band against which the workpiece web is pressable by a pressure medium. A pressure chamber accommodates the pressure medium and adjoins the pressing band, the pressure chamber is sealed with a peripherally closed sealing strip which forms sealing frame, and the sealing frame is loaded in direction toward the pressure band.
Arrangements of the above mentioned general type are known in the art. One of such arrangement is disclosed, for example in the German document DE-OS 33 13 406. In this arrangement the sealing strip is mounted on a rectangular holding frame which is provided with rounded corners. The sealing frame has a constant width over its whole length.
The product is supplied to the arrangement which can be formed as a double band press, and deformed under the action of heat and pressure. Thereby, the product is in a not plastified soft condition in the region of the supply side to the pressure cushion which limits the sealing frame. During a further movement of the product along the pressure cushion, the product is soft and deformable because of the heating. As a result of this, the partial quantity of the product is pressed out over the sealing strips in the region of the longitudinal sides of the pressure cushion. In this region, the tightness between the sealing strips extending in the longitudinal direction and the pressing band is therefore not guaranteed.
During further movement of the product along the pressure cushion, the product is hardened. Therefore, at the discharge region of the pressure cushion, untightness between the sealing frame and pressing band is produced and the pressure medium can flow out of the pressure cushion through the gap between the sealing frame and the pressing band. It is clear that this is highly undesirable.